As a conventional solenoid valve for hydraulic control (e.g. Japanese Unexamined Patent Publication 2002-228036 (Patent Document 1)), for example, a spool typed three-way linear solenoid having a structure as shown in FIG. 4 is known. The solenoid valve 801 in FIG. 4 has a solenoid portion 802 as an electromotive driving portion and a valve portion 804.
The solenoid portion 802 has a solenoid case 821, a molded object 823 mounted on an inner circumference side of the solenoid case 821, and a coil 822 implanted in the molded object 823. On an inner circumference side of the molded object 823, a side ring 837, a spacer 836 and a center post 827 are fixed along an axial direction. On an inner circumference of the side ring 837, a plunger 824 is arranged in an axially movable condition and on an inner circumference of the center post 827, a rod 826 is arranged in an axially movable condition. The spacer 836 is a nonmagnetic member arranged for forming a magnetic gap. Note that the coil 822 is provided with control voltage from a connector 828 protruding out of the solenoid case 821.
The valve portion 804 has a valve sleeve 841, a spool 860, a retainer 845 and a spring 842. The valve sleeve 841 contains the spool 860 within its through-bore, and is formed with an input port in which control fluid flows, a control port which provides control fluid to a load such as automatic gearbox and the like, a drain port and a feedback port, not shown in the figure, on its peripheral wall. The spool 860 is a member arranged in the valve sleeve 841 in an axially movable condition, and is composed of a cylindrical spool shaft and a plurality of lands cylindrically formed with a larger diameter than that of the spool shaft. At a head of the spool 860, a posterior end of the spring 842 mounted in the retainer 845 is mounted, and the spool 860 is always pressed to the direction of the plunger 824 and the rod 826 by elastic force of this spring 842.
In thus-constituted solenoid valve 801, by providing electric current from a control circuit not shown in the figure to the coil 822 of the solenoid portion 802, the coil 822 generates a magnetic field with a desired strength and a desired direction. The electromagnetic force by the magnetic field allows the plunger 824 to move, the rod 826 integrally unified to the plunger 824 contacts with an end face of the spool 860 to press the spool 860 against the elastic force of the spring 842, and the spool 860 moves to the direction of the spring 842 in the valve sleeve 841.
When the amount of the electric current provided to the coil 822 is relatively increased to act large electromagnetic force to the plunger 824, the spool 860 moves toward the spring 842 in the valve sleeve 841 of the valve portion 804, and the amount of the control fluid flowing from the control port to the drain port is increased. On the other hand, when the amount of the electric current provided to the coil 822 is relatively decreased to reduce electromagnetic force acted onto the plunger 824, the spool 860 moves toward the solenoid portion 802 in the valve sleeve 841, and the amount of the control fluid flowing from the input port to the control port is increased.